Atrial fibrillation is a condition that affects large groups of people, with new patients being diagnosed each year. These patients have a lower quality of life as well as having up to a seven times increase in the likelihood of heart attacks or strokes. Current therapies include drug treatment or defibrillation, both palliative forms of treatment. Over the past few years, a number of research groups have been investigating curative treatment involving ablative techniques using radio frequency (RF), ultrasound, laser or microwave energy, or cryoablation techniques.
Ablation therapy, while being promising, requires complex catheter designs. Such catheters also have to be reasonably thin to be manoeuvred through a patient's vascular system.
A current approach is the use of a catheter in the shape of a lasso that has a number of electrodes used for diagnostic purposes only. The lasso is positioned through the left atrium of the heart in pulmonary veins. As the lasso is round in shape, it surrounds the inside of the vein. Different sizes of catheters are required depending on the size and shape of the ostium.
Naturally, it is not possible to steer a catheter in a lasso shape through the vasculature of the patient and it is necessary to form the lasso at the site of the patient's heart to be treated. It is difficult to steer the catheter through the patient's vasculature and also to form a distal region of the catheter into the required lasso shape.
Steerable catheters have, in the past, made use of a metal strip or shim contained within the distal end of the catheter as a portion of a steering device. One or more pull wires are connected to the metal strip. Manipulation of these pull wires causes deflection of the distal end of the catheter.
Such a design is complex and difficult to manufacture. In particular, the numerous components must be assembled and joined together, typically by hand.
In addition, a catheter lumen often contains a steering device along with other elements such as electrical conductors and/or irrigation conduits. Therefore, space within the lumen is at a premium.